1. Technical Field
The present disclosure relates to the production of unsaturated hydrocarbons, and more particularly to a selective hydrogenation catalyst and methods of making and using same.
2. Background
Unsaturated hydrocarbons such as ethylene and propylene are often employed as feedstocks in preparing value added chemicals and polymers. Unsaturated hydrocarbons may be produced by pyrolysis or steam cracking of hydrocarbons including hydrocarbons derived from coal, hydrocarbons derived from synthetic crude, naphthas, refinery gases, ethane, propane, butane, and the like. Unsaturated hydrocarbons produced in these manners usually contain small proportions of highly unsaturated hydrocarbons such as acetylenes and diolefins that adversely affect the production of subsequent chemicals and polymers. Thus, to form an unsaturated hydrocarbon product such as a polymer grade monoolefin, the amount of acetylenes and diolefins in the monoolefin stream is typically reduced. For example, in polymer grade ethylene, the acetylene content typically is less than about 2 ppm.
One technique commonly used to reduce the amount of acetylenes and diolefins in an unsaturated hydrocarbon stream primarily comprising monoolefins involves selectively hydrogenating the acetylenes and diolefins to monoolefins. This process is selective in that hydrogenation of the monoolefin and the highly unsaturated hydrocarbons to saturated hydrocarbons is minimized. For example, the hydrogenation of ethylene or acetylene to ethane is minimized.
One challenge to the selective hydrogenation process is the potential for runaway reactions that lead to the uncontrollable reduction of ethylene to ethane. One methodology to minimize runaway reactions is to increase the amount of selectivity enhancers in the hydrogenation catalyst. Thus, catalyst preparations may comprise one or more selectivity enhancers. Selectivity enhancers are materials such as alkali metal halides that increase the catalyst selectivity for the hydrogenation of highly unsaturated olefins to unsaturated olefins. The use of additional amounts of selectivity enhancers, also termed increased loadings, may lead to improved catalyst selectivity; however, the increased loadings may have drawbacks such as decreased catalyst activity. Therefore, a need exists for a hydrogenation catalyst that has a desired selectivity and activity.